The conventional method of determining the carbon content by thermal analysis is to measure the cooling curve. When the temperature falls below the liquidus line (line AB on the FeC diagram) the curve shows a relatively pronounced kink i.e. the "arrest point". The temperature of this "arrest point" is dependent upon the carbon content of the melt which can be determined from existing tables and calibration curves derived from the iron carbon phase diagram.
The known method requires very sensitive accurately calibrated measuring equipment, since a small error in the absolute temperature measurement may result in a large error in the determination of carbon.